We define our historical eras, naturally, by things that we associate with them. We started making tools in the Bronze Age, the plague was in the Dark Ages, we strapped dogs and monkeys to rockets in the Space Age, and for a brief time in the '90s people wore shirts that changed color when they sweat.
But not everything is so cut and dried; sometimes things that you only thought existed in the black and white world were still around until just a few years ago. For instance ...